1. Field of the Invention
The invention relates to a medical device for treating sleep apnea, specifically a nasal continuous positive airway pressure (CPAP) device. CPAP involves the administration of air under pressure to a patient through a mask or any other suitable connection means. The positive air pressure from the CPAP device forces the upper respiratory tract open, prevents collapse of the pharynx and tongue over the air passage, and aids in increasing lung volume which improves the upper airway muscle dilation tone as air is exhaled.
2. Description of the Prior Art
Sleep apnea syndrome is a sleep disorder characterized by recurrent, prolonged episodes of apnea (cessation of breathing) throughout the night causing excessive daytime sleepiness (hypersomnolence). While occasional periods of apnea during sleep are relatively harmless and occur in most adults, those suffering from sleep apnea syndrome experience episodes of breathing obstruction that last more than 10 seconds and which occur an average of 5 times per hour. Many sleep apnea patients experience apneic periods lasting more than 30 seconds, and have hundreds of such episodes throughout the night causing them to spend most of the night in airway obstruction.
Three types of sleep apnea occur:
1. obstructive sleep apnea, in which breathing is blocked by an obstruction of the upper respiratory tract producing respiratory effort, but no air flow, PA1 2. central sleep apnea, a less common condition, in which the respiratory signals from the brain temporarily cease to stimulate respiratory effort, and PA1 3. mixed sleep apnea, in which elements of both obstructive and central sleep apnea are present, usually as a central component followed by an obstructive component.
A number of conditions are thought to contribute to the sleep apnea syndrome. As would be expected, obstructive sleep apnea is associated with factors that would easily cause obstruction of the upper respiratory tract. There are four major factors contributing to obstructive sleep apnea. Poor muscle tone in the muscles lining the upper airway results in inadequate muscle tone to assist in keeping the airway open during inspiration. The presence of abnormal structures that impinge on airways such as large adenoids and tonsils in children, or bulky pharyngeal tissues in obese adults may reduce airway space, and patients with malformations of the chin, or with enlarged tongues may not be able to accommodate their tongues, causing them to fall back and block the airway. Excessive length of the soft palate and uvula results in reduction in the nasopharyngeal space and reduction in air flow. Restricted air flow through the nose creates increased negative pressure during inspiration which draws together the flaccid tissues in the collapsible part of the airway.
Several devices have been used to treat obstructed sleep apnea. Nasopharyngeal tubes have been developed which are inserted into the upper airway to reach past the point of obstruction in order to maintain upper airway patency during sleep. While they do work, nasopharyngeal tubes are extremely uncomfortable, and most patients cannot tolerate them on a long-term basis.
A number of tongue restraining devices (TRDs) have been developed to prevent the tongue from obstructing the airway during sleep. One newer TRD acts to pull the tongue away from the posterior wall of the pharynx, and appears to relieve sleep apnea to some degree in some patients. Investigators are unsure if patients will comply with long-term TRD therapy, and speculate that it may serve as a noninvasive method for temporary relief of apnea while patients are attempting weight reduction and other behavior modification changes.
There have been several surgical approaches to try to diminish the severity of obstructive sleep apnea. Tracheostomy, for example, was one of the first approaches to surgically treat apnea. In this procedure, a tracheostomy tube bypasses the airway obstruction and allows a patient to breathe. Another surgical procedure, called Uvulopalatopharyngoplasty or UPPP, removes redundant tissue in the patient's airway. The UPPP is a relatively new surgical approach which is currently being documented for its effectiveness. Another technique, Maxillomandibular and hyoid advancement, is a complicated multifaceted surgery that is presently being documented in medical journals. Although this particular type of surgery looks encouraging, its practice will be limited due to the cost and preclusion criteria for the surgery. The cost of surgery and the limited effectiveness of each of these procedures has thus limited its use.
The most promising medical device currently available for sleep apnea is nasal continuous positive airway pressure (CPAP). CPAP involves the administration of air under pressure through a nasal mask. Air pressure is measured in centimeters of water (cm H.sub.2 O), and CPAP typically delivers air to the patient at a pressure of 3.0 to 18 cm H.sub.2 O. The exact means by which CPAP acts to prevent or reduce sleep apnea is not fully understood. However, CPAP appears to act as a pneumatic splint on the pharyngeal area, that is, the positive air pressure from the CPAP device forces the upper respiratory tract open and prevents collapse of the pharynx and tongue over the air passages. In addition, it is thought that CPAP aids in increasing lung volume which improves the upper airway muscle dilation tone as air is exhaled.
In studies of patients treated with CPAP for sleep apnea, the use of a CPAP device has been found to produce a significant reduction or elimination of apnea, less severe oxygen desaturation during REM sleep, and an increase in the amount of time spent in deeper sleep. Several studies have documented a high rate of patient compliance (85%-95%) with home nasal CPAP systems. CPAP is usually administered initially in the sleep disorders center. After a sleep study is conducted and it is determined that the individual may benefit from CPAP (it is determined that he has either obstructive or mixed apnea), the patient is then fitted with a CPAP device the same or a following night. As the patient starts to obstruct, the CPAP is increased to maintain the airway. This continues through all stages of sleep, including and in particular REM sleep, and is used to determine the CPAP pressure settings for the individual patient which will maintain an open airway.
If CPAP therapy is successful in the sleep lab, the patient is sent home on CPAP therapy with regular follow-ups (either visits to the sleep lab or at-home monitoring) at 6-12 month intervals to assess patient compliance and improvement. When compared to other forms of therapy, the complications with nasal CPAP are relatively minor and include a reduction of sinus draining, drying of the nasal membrane (mucosa), and inflammation of the nasal mucosa (rhinitis). The available data regarding this treatment approach have led many physicians to conclude that CPAP is the best choice for therapy in patients with sleep apnea.
A CPAP device sold under the brand name Tranquility.RTM. is described in the brochure entitled "Tranquility.RTM.Nasal CPAP System", distributed by Healthdyne Corp., and is designed to eliminate some of the problems inherent in devices using CPAP valves. This device replaces the CPAP valve with a semiconductor pressure transducer and an electronic servo-control system that adjusts blower speed to maintain pressure. The device maintains pressure to calibrated setpoints so that the user knows what pressure would be delivered without having to adjust the machine while measuring the output pressure with an additional device.